As well known, a vitrectomy surgical operation is an ophthalmic operation performed when the vitreous has become opaque due to hemorrhages, e.g., after a proliferative diabetic retinopathy, inflammation or due to a traction force applied to the retina or the presence of membranes or foreign objects within the eyeball. The vitrectomy surgical operation consists of both removing small fragments of membranes from the retinal surface and the vitreous and replacing it by using an equivalent means, called “vitreous substitute”.
The basic device to perform said vitrectomy operation is the vitrectomy probe, which is a pneumatic guillotine configured for performing the aforementioned removal and excision operations. The vitrectomy probe is provided with:                a handgrip shaped to allow the operator to properly handle the tool;        an outer tube comprising a slot manufactured on its own lateral surface proximate to one end of the outer tube itself;        an inner tube that is inserted within the outer tube;        a command system which creates a depression, i.e. a vacuum degree, within the outer tube and the inner tube, and causes the inner tube to relatively move with respect to the outer tube.        
In particular, the command system, thanks to the synergy of the abovementioned depression and relative movement, enables the vitrectomy probe to suck in the vitreous in such a way that the vitreous fragments, attracted by the suction, are cut by the moving edge of the inner tube when the edge overlaps the slot manufactured on the lateral surface of the outer tube.
Examples of a vitrectomy probe can be found in DE 102010 and in U.S. Pat. No. 5,106,364.
However, the above mentioned prior art devices have some relevant drawbacks.
A first significant disadvantage is that the vitrectomy probes are very difficult to be used and great expertise and care are required to the surgeon during the surgical operation, because it is very hard to adjust the suction flow rate in order to perform accurate excision.
In particular, the size and the number of the fragments of vitreous excised by the vitrectomy probe only depend upon the movements and the position of the probe, while the probe is located inside the eye and, therefore, they only depend upon the surgeon skill.
Thus, another drawback is that the surgical vitrectomy operation takes a very long time, since the vitrectomy probe must be extremely accurately handled, which requires very slow movements.
The operation takes a long time also because, in order to reduce the risk of errors, the vitrectomy probes must be set to a very low removal rate, wherein the flow rate periodically changes from zero to a maximum value in a substantially sinusoidal law, due to the slots overlap variation.
Another disadvantage is that the costs of the vitrectomy operations are rather high, due to long duration.
For example, in WO2010118172 a rotary inner tube acts as the internal port of standard vitrectomy probes, but, due to the length of the helical grooves, the suction force is reduced by such features as friction, turbulences, and so on. Moreover, the system can be applied only to rotary vitrectomy probes and the suction has a sinusoidal behaviour whose maximum is limited by the above-mentioned features.
In WO2012059092 and in U.S. Pat. No. 5,106,364, which appears to be the patents most closely related to the invention, the suction is increased through multiples ports made both on the external tube and on the internal one. These solutions can be applied to both rotary and linear/oscillating vitrectomy probes. However, in the described realizations, the suction has a square-wave behaviour, and the traction force continues to pulse accordingly. Moreover, the axial extension of the ports on the external tube is increased, which causes a loss of precision.